End of stroke detection for electromagnetic pump

ABSTRACT

Detection of end of stroke for an electromagnetic pump is performed using, for example, a calculated first flux derivative.

TECHNICAL FIELD

The present invention relates generally to electromagnetic pumps (e.g.,such as those used in infusion devices that are implantable or otherwiseconnected to patients), as well as to methods relating to suchelectromagnetic pumps.

BACKGROUND OF THE INVENTION

Infusion devices are typically used to deliver an infusion medium, suchas a medication, to a patient. Implantable infusion devices are designedto be implanted in a patient's body to administer an infusion medium tothe patient at a regulated dosage, over a period of time. Externalinfusion devices may be designed to be portable, for example, to be wornoutside of the patient's body and connected to the patient by acatheter. Other fauns of infusion devices are non-portable devices,typically for use in a controlled environment, such as a hospital.

Electromagnetic pump mechanisms (e.g., mechanisms that include a coiland an actuator which moves relative thereto) are used in infusiondevices to selectively drive infusion medium, for example, to a patient.Various forms of electromagnetic pumps have been developed for use ininfusion devices operating in external or implant environments. Forexample, one or more various electromagnetic pump mechanisms aredescribed in U.S. Pat. No. 4,594,058 issued 10 Jun. 1986 to Fischell,entitled “Single valve diaphragm pump with decreased sensitivity toambient conditions”; U.S. Pat. No. 4,684,368 issued 4 Aug. 1987 toKenyon, entitled “Inverted pump”; U.S. Pat. No. 4,569,641 issued 11 Feb.1986 to Falk et al., entitled “Low power electromagnetic pump”; U.S.Pat. No. 4,568,250 issued 4 Feb. 1986 to Falk et al., entitled “Lowpower electromagnetic pump”; U.S. Pat. No. 4,636,150 issued 13 Jan. 1987to Falk et al., entitled “Low power electromagnetic pump”; U.S. Pat. No.4,714,234 issued 22 Dec. 1987 to Falk et al., entitled “Low powerelectromagnetic valve”; U.S. Pat. No. 6,595,756 B2 issued 22 Jul. 2003to Gray et al., entitled “Electronic control system and process forelectromagnetic pump”; U.S. Pat. No. 6,997,921 B2 issued 14 Feb. 2006 toGray et al., entitled “Infusion device and driving mechanism for same”;U.S. Pat. No. 7,186,236 B2 issued 6 Mar. 2007 to Gibson et al., entitled“Infusion device and inlet structure for same”; U.S. Pat. No. 6,805,693B2 issued 19 Oct. 2004 to Gray et al., entitled “Infusion device anddriving mechanism for same”; and U.S. Pat. No. 6,652,510 B2 issued 25Nov. 2003 to Lord et al., entitled “Implantable infusion device andreservoir for same.”

Typically, electromagnetic pump configurations, such as those describedin the above-referenced patents, employ a conductive coil of the pumpcoupled to a power source using control electronics. The coil isselectively energized by the power source and control electronics (e.g.,using a controller and a switch) to create an electromagnetic fieldwhich operates on a moveable actuator (e.g., armature and piston). Whenthe coil is energized, the electromagnetic field causes the actuator tomove, for example, against the force of a spring, toward a strokeposition. When the coil is then de-energized, the spring force, forexample, returns the actuator to the position it had prior to energizingthe coil. By moving the actuator between the energized stroke positionand its return position, a pumping action is accomplished by theelectromagnetic pump.

In many circumstances, such as when electromagnetic pumps are used ininfusion devices, the electromagnetic pumps may be operable for extendedperiods of time with a limited power supply. For example,battery-powered infusion devices may be implanted in or otherwiseconnected to patients to deliver medication at controlled intervals overa prolonged period of time. As battery power supplies have limitedcapacities, such devices may require multiple replacements of batteriesover their operational life. In the case of an electromagnetic pump usedin an implanted infusion device, a replacement of a battery may requirethe surgical removal of the infusion device. Even with external devices,the replacement of a battery may require specialized tools, parts, orskills which necessitate the services of a specialist or trainedtechnician. As such, in the art of electromagnetic pumps, for example,that are used in infusion devices, there is a desire to make efficientuse of the power supply.

In many prior infusion devices, capacitor discharge power controlcircuits are used as the power source for the electromagnetic pump.Generally, such power control circuits include a capacitor that ischarged by a battery and selectively discharged to the coil of theelectromagnetic pump to power the pump operation. For example, eachdischarge of the capacitor delivers an electrical power pulse to thecoil sufficient to energize the coil and cause the pump to make onecomplete stroke. The capacitor is charged by the battery between pumpstrokes.

To operate the electromagnetic pump under generally all expected powerload conditions, the capacitor size of the power control circuits isgenerally selected such that the power output per complete discharge issufficient to operate the pump in the greatest expected power loadcondition. As a result, sufficient power to operate the pump in thegreatest expected load condition is provided to the pump, even when thepump is not operating under the greatest expected load. Such a completepower discharge at every pump stroke, independent of the pump's powerneeds, results in a waste of electrical power.

Various manners of attempting to decrease power consumption have beenattempted. For example, generally, control signal circuitry isprogrammed or configured to generate a signal to control the closure ofa switch coupling the power source to the electromagnetic pump upon theoccurrence of one or more various events. For example, such events mayinclude the expiration of a predetermined time period after initiationof a stroke and prior to initiation of a subsequent stroke. However,even prior to the expiration of a predetermined time period, end ofstroke of the electromagnetic pump generally occurs. Allowing dischargeof the capacitor (e.g., application of power to the electromagneticpump) through expiration of the predetermined time period even when endof stroke has occurred would be an expenditure of unnecessary power.

As such, various techniques have been described for use in controllingthe capacitor discharge to the electromagnetic pump to reduce powerconsumption. For example, in U.S. Pat. No. 6,595,756 to Gray et al., adetector for detecting the end of a pump stroke is described such that apower control circuit may cut off power to the pump coil prior to thedetected end of the pump stroke. As described therein, for example, theback electromotive force (back EMF) of the coil is detected to determinewhen or where the actuator is capable of completing its full strokemotion after the capacitor discharge is cut off. By detecting ormonitoring the back EMF generated in the coil, a suitable cut off timemay be determined. Further, as described therein, a sharp positive riseor a change in direction of a coil current can indicate actuatordeceleration that occurs at the actual end of the actuator's forwardstroke. A suitable capacitor cut off point can also be selected basedthereon.

SUMMARY OF THE INVENTION

The present invention provides for one or more methods of detecting theend of stroke for an electromagnetic pump. Using such information, powerapplied to the electromagnetic pump may be selectively cut to reduceenergy consumption. For example, in one or more embodiments, the presentinvention uses both the coil potential and the coil current, as well asmathematical relationships between them, and the changing inductance, toprovide reliable detection of end of stroke and also provide strokeposition information for the electromagnetic pump (e.g., actuatorposition information which can be used as diagnostic information for thepump).

An electromagnetic pump system (e.g., such as a pump that is part of animplantable medical device) according to one embodiment of the presentinvention includes an electromagnetic pump. The pump includes a coilthat can be energized to produce a pump stroke, wherein theelectromagnetic pump further includes an actuator moveable in responseto the energization of the coil. A power source is connected toselectively energize the coil of the electromagnetic pump, wherein thepower source applies a source electrical potential to the coil to pass acoil current therethrough. A voltage sense device senses the sourceelectrical potential applied to the coil and a current sense devicesenses the coil current. Further, the system includes controlelectronics to detect the end of a pump stroke based on a change in fluxover time calculated as a function of sensed coil current and sourceelectrical potential.

In one embodiment of the system, the control electronics calculatesU_(source)−(R_(coil)*I_(coil)) over time corresponding to the change offlux over time, where U_(source) is source electrical potential,R_(coil) is the resistance of the coil, and I_(coil) is the coilcurrent. Further, in another embodiment, the control electronicsperforms peak detection to detect a peak inU_(source)−(R_(coil)*I_(coil)) as calculated over time corresponding tothe end of a pump stroke.

An implantable infusion device for delivery of infusion medium accordingto one embodiment of the present invention includes a drive mechanism.The drive mechanism includes a coil that can be energized to produce apump stroke, wherein the drive mechanism further includes an actuatormoveable relative to the coil in response to the energization of thecoil to deliver infusion medium. A power source is connected toselectively energize the coil of the electromagnetic pump, wherein thepower source applies a source electrical potential to the coil to pass acoil current therethrough. One or more sense devices sense the sourceelectrical potential applied to the coil and the coil current. Controlelectronics of the device detects the end of a pump stroke based on achange in flux over time calculated as a function of sensed coil currentand source electrical potential. The control electronics includes aswitch device connected between the power source and the coil to connectthe power source to the coil at the initiation of a pump stroke anddisconnect the power source from the coil upon detection of an end ofthe pump stroke.

Another embodiment of an electromagnetic pump system according to thepresent invention includes an electromagnetic pump. The pump includes acoil that can be energized to produce a pump stroke, wherein theelectromagnetic pump further includes an actuator moveable in responseto the energization of the coil. A power source is connected toselectively energize the coil of the electromagnetic pump, wherein thepower source applies a source electrical potential to the coil to pass acoil current therethrough. A voltage sense device senses the sourceelectrical potential applied to the coil and a current sense device forsensing the coil current. Control electronics calculates inductance ofthe coil as a function of sensed coil current and source electricalpotential when the actuator is not moving for use in determiningposition of the actuator.

In one embodiment of the system, the control electronics calculates(U_(source)−(R_(coil)+R_(source))*I_(coil))/d/dt I_(coil) for use indetermining position of the actuator.

A method for use in controlling an electromagnetic pump (e.g., anelectromagnetic pump that includes a coil that can be energized by apower source to produce a pump stroke and an actuator moveable inresponse to the energization of the coil) according to one embodiment ofthe present invention includes applying a source electrical potential tothe coil to pass a coil current therethrough to provide a pump stroke.The source electrical potential applied to the coil and the coil currentis sensed. The method further includes detecting the end of the pumpstroke based on a change in flux over time calculated as a function ofsensed coil current and source electrical potential.

In one embodiment, selectively applying a source electrical potential tothe coil includes connecting the power source to the coil at theinitiation of a pump stroke and disconnecting the power source from thecoil upon detection of an end of the pump stroke. Further, the pumpstroke may deliver infusion medium.

In another method for use in controlling an electromagnetic pump (e.g.,an electromagnetic pump that includes a coil that can be energized by apower source to produce a pump stroke and an actuator moveable inresponse to the energization of the coil) includes applying a sourceelectrical potential to the coil to pass a coil current therethrough toprovide a pump stroke, sensing the source electrical potential appliedto the coil, and sensing the coil current. Further, the method includescalculating inductance of the coil as a function of sensed coil currentand source electrical potential for use in determining position of theactuator.

Yet further, back EMF may also be calculated as a function of sensedelectrical potential and coil current for use in detecting end of pumpstroke. Such calculated back EMF may be used alone to detect end of pumpstroke or may be used to verify an already detected end of stroke.

The above summary is not intended to describe each embodiment of everyimplementation of the present invention. Rather, a more completeunderstanding of the invention will become apparent and appreciated byreference to the following detailed description and claims in view ofthe accompanying figures of the drawing.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be further described with reference to thefigures of the drawing, wherein:

FIG. 1 is a perspective view of an implantable infusion device accordingto one embodiment of the present invention.

FIG. 2 is a perspective view of a drive mechanism or electromagneticpump for an implantable infusion device according to one embodiment ofthe present invention.

FIG. 3 is a cross-section view of one exemplary embodiment of theelectromagnetic pump of FIG. 2, in a retracted position or state.

FIG. 4 is a cross-section view of the exemplary electromagnetic pumpembodiment of FIG. 3, in a forward stroke position or state.

FIG. 5 is a generalized block diagram of one exemplary embodiment of anelectromagnetic pump, power source, and control electronics according tothe present invention.

FIG. 6 is a graphical diagram of exemplary voltage characteristics of apower discharge capacitor controlled according to one embodiment of thepresent invention.

FIG. 7 is a graphical diagram of exemplary current characteristics of acoil connected to a power discharge capacitor controlled according toone embodiment of the present invention.

FIG. 8 is a graphical diagram of exemplary voltage characteristics of apower discharge capacitor, current characteristics of a coil operativelyconnected to the power discharge capacitor, and a calculated first fluxderivative waveform according to one embodiment of the presentinvention.

FIG. 9 is a graphical diagram of exemplary current characteristics of acoil connected to a power discharge capacitor, calculated first fluxderivative waveforms, and position information according to one or moresimulated embodiment of an electromagnetic pump according to the presentinvention.

FIG. 10 is a graphical diagram of exemplary voltage characteristics of apower discharge capacitor, current characteristics of a coil connectedto the power discharge capacitor, a calculated first flux derivativewaveform, and position information according to one or more embodimentsof an electromagnetic pump according to the present invention.

FIG. 11 is a graphical diagram of calculated back EMF voltage forillustrating the use of back EMF in the detection of end of pump strokeaccording to one or more embodiments of an electromagnetic pumpaccording to the present invention.

FIG. 12 is a graphical diagram of exemplary inductance waveforms for usein illustrating the determination of position of an actuator of anelectromagnetic pump according to one or more embodiments of the presentinvention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the following detailed description of the illustrative embodiments ofthe invention, references are made to the accompanying figures of thedrawing which form a part hereof, and in which are shown, by way ofillustration, specific embodiments in which the invention may bepracticed. It is to be understood that other embodiments may be utilizedand structural changes may be made without departing from the scope ofthe present invention.

As described herein, the present invention relates generally toelectronic control systems, configurations, and processes forelectromagnetic pumps. Embodiments of the present invention relate tosuch systems, configurations, and processes for efficient utilization ofpower and reduction of electrical power consumption requirements inelectromagnetic pumps, particularly as they relate to the detection ofan end of pump stroke, as well as employing such detection for thecontrol of electromagnetic pumps. Yet further, other embodiments relateto the use of other calculated information for determining variouscharacteristics of an electromagnetic pump, such as the position of anactuator in the electromagnetic pump (e.g., relative to a coil thereofor other structure of pump). Yet further, other embodiments relate toinfusion devices for delivery of infusion medium (e.g., implantableinfusion devices) or other medical devices that may employelectromagnetic pumps utilizing the techniques described according tothe present invention.

In general, one or more embodiments according to the present inventionuse both the electrical potential applied to a coil of anelectromagnetic pump and the current passing through the coil, as wellas the mathematical relationship between them, and the changinginductance, to provide reliable detection of end of stroke and, also, inone or more embodiments, provide stroke positioning information. Variousalgorithms are described herein to provide information for the detectionof the end of a pump stroke, and, also, in one or more embodiments,information related to such a pump stroke (e.g., position information ofthe actuator of the pump). For example, such algorithms may be referredto herein as a first flux derivative algorithm (e.g., for use indetection of end of pump stroke), back electromotive force (back EMF)algorithm (e.g., for use in detection of end of pump stroke), and coilinductance variation algorithm (e.g., for use in detection of positionof the actuator of the pump).

FIG. 1 shows one embodiment of an implantable infusion device 10according to the present invention. The illustrative infusion device 10is configured to be surgically implanted into a patient. A catheter maybe connected to the pump so as to deliver infusion medium to a patient,for example, by feeding infusion medium to a particular target site(e.g., location in the venous system, within the spinal column, or inthe peritoneal cavity) of the patient.

As described herein, one or more embodiments of the present inventionmay be configured for enhancing implantability and prolonged usage onceimplanted (e.g., battery life). Further, one or more embodiments may beimplemented as external infusion devices, which connect to patientsthrough suitable catheter devices, or the like.

Further, one or more embodiments may be used in other contexts fordelivery of a medium into other suitable environments. Therefore, forpurposes of simplifying the present disclosure, the term patient is usedherein to refer to the entity or environment in which an implantabledevice is implanted or to which an external device is connected. Also,the term “infusion medium” is used herein to refer to any suitablemedium delivered by the device 10 (e.g., medicaments, drugs, treatmentmedium, etc.).

The illustrative device 10 is configured as a single unit, containing,for example, an infusion medium reservoir, a pump mechanism, and anelectronic control system, in a single relatively compact package orhousing 12. However, other embodiments may employ reservoirs, pumpmechanisms, power sources, and control systems in multiple discreteunits operatively connected together by suitable conduits.

The infusion device 10 includes a generally disc-shaped housing 12.While a generally circular disc-shaped embodiment is illustrated in FIG.1, it will be understood that further embodiments of the invention mayemploy housings of other shapes including, but not limited to, oval,oblong, rectangular, or other curved polygonal shapes. In implantabledevice embodiments, the housing 12 is made of a biocompatible materialand is relatively small to reduce or minimize patient trauma duringimplant surgery and after implantation.

The housing 12 includes a reservoir housing portion 13 containing areservoir for holding a volume of infusion medium, such as, but notlimited to, a liquid medication to be administered to a patient. Thehousing 12 includes a further housing portion 14 located above thereservoir housing portion 13, in the orientation shown in FIG. 1, forcontaining an electromagnetic pump 20 and an electronic control system22 (e.g., power source and control electronics) as described herein. Onewill recognize that various types of housings and reservoirs may beutilized according to the present invention and the present invention isnot limited to the illustrative housings and reservoirs shown herein.

The housing 12 has an outlet 16 through which the infusion medium may beexpelled. When the device 10 is implanted in a patient or connectedexternally to a patient, a catheter may be connected to the outlet 16through which infusion medium may be expelled (e.g., into the patient'sbloodstream or to a selected location of the patient's body).

Infusion device 10 also includes an inlet structure 15 which provides acloseable and sealable fluid path to the reservoir and the reservoirhousing portion 13 of the housing 12. For example, the inlet structureprovides a port for receiving a needle through which fluid may betransferred to the infusion device 10, for example, to fill or refillthe reservoir of the device. One or more various differentconfigurations of inlet and outlet structures may be employed accordingto the present invention, and the present invention is not limited toany particular inlet and outlet structure.

The infusion device 10 includes an electromagnetic pump 20 (e.g., adrive mechanism) and an electronic control system 22 located in ahousing portion 14. The electromagnetic pump 20 is connected between thereservoir in the reservoir housing portion 13 and the outlet 16. Theelectronic control system 22 includes a power source, such as a battery,and control electronics for controlling the electromagnetic pump 20 todeliver infusion medium from the reservoir to a patient in a selectedmanner. The electromagnetic pump 20 may be controlled to deliverinfusion medium in any suitable manner, for example, according to aprogrammed dispensing rate or schedule, or according to an actuationsignal from a sensor, timer, or other suitable source.

For example, according to one or more embodiments herein, theelectromagnetic pump 20 provides delivery of infusion medium byemploying a plurality of pump strokes to drive the infusion medium tothe outlet 16 of the device. Such pump strokes of the electromagneticpump 20 are controlled using control electronics of the electroniccontrol system 22 according to the present invention (e.g., controlledat least in part with detection of end of pump stroke).

As described herein, a number of techniques relating to electromagneticpump configurations and operation are described herein to enhance theefficient use of power. One or more of such techniques, or features, maybe employed in various embodiments of the present invention. Forexample, detection of end of pump stroke may be used to determine theproper time to de-energize the coil of the electromagnetic pump (e.g.,cut off power to the pump upon detection of the end of a pump stroke).

In one or more embodiments, the infusion device 10 is configured suchthat once implanted, it functions for a relatively long period of timeto administer infusion medium to a patient and periodically bereplenished from outside of the patient's body. The operational life ofthe infusion device 10 is, however, limited in part by the capacity ofits power source and the power requirements of the device.

In one or more embodiments, the electromagnetic pump 20 of the infusiondevice 10 is employed to provide reliable pumping action and theoperation thereof is controlled to be highly efficient with respect topower consumption. As such, the operational life of the infusion deviceis improved. Further, electromagnetic pumps controlled according to thepresent invention provide highly efficient use of power, as describedherein, and as such may be operated with smaller power sources (e.g.,power sources including relatively smaller batteries), which can allowthe infusion device to be made smaller.

Generally, electromagnetic pumps employ electromagnetic and mechanicalforces to move between retracted (or quiescent) and forward strokestates to cause infusion medium to be drawn from a reservoir, through apump inlet, and forced out of a pump outlet. Such electromagnetic forcesare generated by the application of an electrical power signal to a coilof the electromagnetic pump which, when energized, operates on anactuator to provide a pump stroke. For example, the actuator may includean armature and a piston. In a retracted state, the actuator ismechanically urged towards a retracted position. When the coil isenergized, the actuator moves to a forward stroke position. The movementof the actuator between retracted and forward states creates pressuredifferentials within the internal chambers and volumes of theelectromagnetic pump to draw infusion medium from the reservoir into thepump inlet and drive medium out of the pump outlet.

In one or more embodiments of the present invention, lowering the powerconsumption requirements of the electromagnetic pump employs thedetection of the end of a pump stroke such that power is notunnecessarily provided to the electromagnetic pump. In other words, upondetection of the end of a pump stroke, power to the electromagnetic pumpcan be turned off, as opposed to applying power to the electromagneticpump after the pump stroke has ended (e.g., after which little or noinfusion medium is driven out of the pump outlet).

One exemplary electromagnetic pump 20 shall be described in furtherdetail with reference to FIG. 2 so as to give context to controltechniques described herein with respect to electromagnetic pumps. Forexample, such an electromagnetic pump 20 is described in detail in U.S.Pat. No. 6,997,921 B2 to Gray et al. issued 14 Feb. 2006, and entitled“Infusion device and driving mechanism for same,” which is incorporatedherein by reference. This is but one example of a type ofelectromagnetic pump for which the control techniques described herein,including detection of end of pump stroke and determination of positioninformation, may be employed.

One will recognize that various other embodiments may employ othersuitable electromagnetic pumps (e.g., other drive mechanismconfigurations). Such control techniques as described herein may beemployed, at least in one or more embodiments, with any electromagneticpump that includes a coil that can be energized to produce a pumpstroke, wherein an actuator is moveable in response to the energizationof the coil, for example, to drive, or otherwise move, a medium from onelocation to another. However, the present invention is not limited toany particular electromagnetic pump configuration.

FIG. 2 shows the electromagnetic pump 20 according to one exemplaryembodiment of the present invention. In this illustrated embodiment, theelectromagnetic pump 20 has a partially cylindrical, disc-shapedconfiguration with extended corners 24 and 25. An inlet 27 is providedat the corner 24 and an outlet 28 is provided at the corner 25. Theinlet 27 may be connected in flow communication with the reservoirportion 13 of the infusion device 10, as shown in FIG. 1, throughsuitable conduit (not shown) within the infusion device 10. Similarly,the outlet 28 may be connected in flow communication with the outlet 16of the infusion device 10, as shown in FIG. 1, through suitable conduit(not shown) within the infusion device 10.

FIG. 3 shows a cross-sectional view of one exemplary embodiment of theelectromagnetic pump 20 in a retracted position or state. FIG. 4 shows across-sectional view of the same electromagnetic pump 20 embodiment in aforward position or state. As described in more detail herein, theelectromagnetic pump 20 employs electromagnetic and mechanical forces tochange (or move) between retracted and forward states to cause infusionmedium to be drawn in through inlet 27 and forced out of the outlet 28.

As shown in the figures, the electromagnetic pump 20 includes a housingmember 30 that has a central hub portion 34 with a central pistonchannel 35. The bottom side of the housing member 30 (with reference tothe orientation shown in FIGS. 3 and 4) includes an opening throughwhich coil wires may pass, as described herein. The bottom side of thehousing member 30 also includes a configuration of recesses and cavitiesfor providing an outlet chamber, an outlet passage, and, in one or moreembodiments, for example, accumulator chambers. The housing member 30,in one or more embodiments, is formed of rigid, biocompatible, andinfusion medium compatible material, having no or low magneticpermeability, such as, but not limited to, titanium, stainless steel(which may be ferritic or non-ferritic), biocompatible plastic, ceramic,glass, or the like.

As shown in FIGS. 3 and 4, a coil cup 32 is located within the annularinterior section of the housing 30. The coil cup 32 has a generallycylindrical shape, open on one end to a hollow annular interior 33. Thecoil cup includes an inner annular wall 90 having an end surface 91 (orinner pole surface). The coil cup 32 has an outer wall 92 having an endsurface 93 (or outer pole surface). The outer wall 92 is connected tothe inner wall 90 by a backiron portion of the cup 32. As describedfurther herein, at the open end of the cup member, the end surfaces 91and 93 of the inner and outer walls 90 and 92, define pole surfaces thatcooperate with pole surfaces on an actuator 40 to provide a path forelectromagnetic flux during a forward stroke of the electromagneticpump.

As assembled, the coil cup 32 is located in the hollow interior of thehousing member 30, with a central portion 34 of the housing 30 extendingthrough the piston channel 36 of the coil cup 32, as shown in FIGS. 3and 4. A coil 38 is located within the hollow, annular interior of thecoil cup 32 and is disposed around the axis A of the annular interior ofthe coil cup 32. The coil cup 32 is provided with an opening 84 throughwhich coil leads 86 extend, as shown in FIGS. 3 and 4.

The coil cup 32 is preferably made of a generally rigid material, havinga relatively high magnetic permeability such as, but not limited to, lowcarbon steel, iron, nickel, ferritic stainless steel, ferrite, otherferrous materials, or the like. The coil 38 comprises a conductive wirewound in a coil configuration. The coil wire may include any suitableconductive material such as, but not limited to, silver, copper, gold,or the like, with each turn electrically insulated from adjacent turnsin the housing. In one preferred embodiment, the coil wire has a squareor rectangular cross-section to allow minimal space between windings,thereby allowing a greater number of coil turns and, thus, improvedelectrical efficiency.

The electromagnetic pump 20 also includes an actuator 40. The actuator40 includes an armature portion 42 and a piston portion 44. The actuatoris preferably made of a generally rigid, biocompatible, and infusionmedium compatible material, having a relatively high magneticpermeability such as, but not limited to, ferrous materials, ferriticstainless steel with high corrosion resistance, or the like.

One will recognize that in accordance with the present invention anytype of coil and actuator configuration forming the electromagnetic pumpmay benefit from the control techniques described according to thepresent invention. As such, the present invention is not limited to anyparticular coil or actuator configuration.

The armature 42 of the actuator, as shown in the illustrative embodimentof FIGS. 3 and 4, cooperates with the inner and outer walls 90, 92 ofthe coil cup 32 to provide a flux path for electromagnetic flux. Thespacing between the pole surfaces on the armature 42 and the polesurfaces on the walls of the coil cup 32 define gaps in the flux path.

With reference to FIGS. 3 and 4, the actuator 40 is arranged with thepiston portion 44 thereof extending through the axial channel 35 of thehousing 30 and with the armature portion 42 positioned adjacent the openside of the coil cup 32. An actuator spring 46 is positioned to forcethe armature portion 42 of the actuator 40 in the direction away fromthe open side of the coil cup 32 to provide a gap between the armature42 and the open side of the coil cup 32. A biocompatible and infusionmedium compatible barrier 48 is located over the open side of the coilcup 32, between the armature 42 and the coil cup 32, to maintain a gapbetween those two members and/or to help seal the annular interior ofthe coil cup 32 and coil 38.

The actuator spring 46 in the illustrated embodiment comprises a coilspring disposed around the piston portion 44 of the actuator 40 adjacentthe armature portion 42. One end of the coil spring abuts the armatureportion 42 of the actuator, while the opposite end of the coil springabuts a shoulder 39 in the piston channel 35 of the housing 30. In thismanner, the actuator spring 46 imparts a spring force between thehousing and the actuator 40 to urge the actuator towards its retractedposition in FIG. 3.

The electromagnetic pump 20 further includes a cover member 50 whichattaches to the housing member 30, over the open side of the housingmember 30 and the barrier 48. The cover member 50 is preferably made ofgenerally rigid, biocompatible, and infusion medium compatible material,having a relatively low magnetic permeability (being relativelymagnetically opaque) such as, but not limited to, titanium, stainlesssteel, biocompatible plastic, ceramic, glass, or the like.

The cover member 50 defines an interior volume 51 between the barrier 48and the inner surface of the cover member 50. The armature portion 42 ofthe actuator 40 resides within the interior volume 51 when the cover 50is attached to the housing 30, such as shown in FIGS. 3 and 4. Asdescribed below, the actuator 40 is moveable in the axial directionwithin the volume 51, between the retracted position shown in FIG. 3 anda forward stroke position shown in FIG. 4. This movement is created bythe action of electromagnetic force generated when a current is passedthrough the coil 38 and the mechanical return action of the actuatorspring 46 (e.g., a pump stroke).

An adjusting plunger 52 is located within the cover 50 for contactingthe armature portion 42, when the armature portion is in the fullyretracted position shown in FIG. 3, and to set the retracted orretracted position of the armature. In one or more embodiments, a sealmay be disposed between the plunger 52 and the cover member 50, forexample, a flexible diaphragm 59 may be coupled to the inside surface ofthe cover 50 and sealed around the opening through which the plunger 52extends.

The cover member 50 includes the inlet 27 of the electromagnetic pump 20which has an inlet opening 54 in fluid flow communication with theinterior volume 51, as described herein. The inlet opening 54 connectsin fluid flow communication with the reservoir of an infusion device 10(FIG. 1) to receive infusion medium from the reservoir. Connection ofthe inlet opening 54 and the reservoir may be through any suitableconduit.

The inlet opening 54 provides a flow to an inlet chamber 56 formed inthe cover member 50 adjacent the inlet opening. A filter or screenmember, such as a porous or screen material 58, may be disposed withinthe inlet chamber 56 between the inlet opening 54 and inlet port 60 tothe volume 51. A one-way inlet valve (not shown) to allow medium to flowinto but not out of the interior volume 51 through the inlet opening 54may also be provided in the flow path between the inlet opening 54 andthe inlet port 60, or within inlet port 60. Further, the cover member 50may be provided with an inlet cover 62 that, when removed, allows accessto the inlet chamber 56.

As shown in FIGS. 3 and 4, the piston portion 44 of the actuator 40extends through the axial channel 35 in the housing 30, toward an outletchamber 64 at the end of the axial channel 35. The channel 35 has aninside diameter which is larger than the outside diameter of the pistonportion 44. As a result, an annular volume is defined between the pistonportion 44 and the wall of the axial channel 35, along the length of theaxial channel 35. Infusion medium may flow through the annular volume,from the volume 51 within the cover 50 to a piston chamber 65 locatedbetween the free end of the piston portion 44 and a valve member 66 of avalve assembly 67. In one or more embodiments, the radial spacingbetween the piston portion 44 and the wall of the channel 35 is selectedto be large enough to provide a suitable flow toward the piston chamber65 to refill the piston chamber 65 (during a return stroke of the pistonportion), but small enough to sufficiently inhibit backflow of mediumfrom the piston chamber 65 (during a forward stroke of the pistonportion).

The valve assembly 67 in the embodiments of FIGS. 3 and 4 includes thevalve member 66, a valve spring 68, and support ring 70. The valvemember 66 is located within the outlet chamber 64 and, as shown in FIG.3, is positioned to close the opening between the axial channel 35 andthe outlet chamber 64 when the actuator 40 is in the retracted position.In FIG. 4, the valve member 66 is positioned to open a flow passagebetween the axial channel 35 and the outlet chamber 64. The valve spring68 is located within the outlet chamber 64 to support the valve member66. Spring 68 imparts a spring force on the valve member 66 in thedirection toward piston 44, urging the valve member 66 toward a closedposition to block the opening between the axial channel 35 and theoutlet chamber 64. The valve spring 68 is spaced from a valve cover 72by a ring 70. The valve cover 72 is sealed to the housing 30 to enclosethe outlet chamber 64. The ring 70 and spring 68 characteristics aresuch that sufficient forces urge the valve member 66 into a suitablysealed or closed position, as shown in FIG. 3, yet allow the movementforce of the piston portion 44 (caused by electromagnetic forcegenerated by the coil) to overcome the spring force and open the valvemember 66, as shown in FIG. 4.

In operation, the electromagnetic pump 20 employs electromagnetic andmechanical forces to move between retracted (FIG. 3) and forward (FIG.4) positions to cause infusion medium to be drawn into and driven out ofelectromagnetic pump 20 in a controlled manner. The electromagnetic pump20 is controlled by an electronic control system, such as electroniccontrol system 22 as shown in the infusion device in FIG. 1, and ofwhich illustrative embodiments shall be described with reference hereinto the general diagram of FIG. 5.

In the retracted position, the spring 46 urges the actuator 40 towardits retracted position shown in FIG. 3. When the coil 38 is energized toovercome the spring force of spring 46, the actuator 40 moves to itsforward stroke position shown in FIG. 4. The movement of the actuator 40between retracted and forward positions creates pressure differentialswithin the internal chambers and volumes of the electromagnetic pump 20to draw medium into the inlet 27 and drive medium out of the outlet 28.

For example, when the coil 38 is deactivated (not energized or notenergized in a manner to overcome the spring force of spring 46), theactuator 40 is held in its retracted position (FIG. 3) under the forceof spring 46. When the coil is deactivated immediately following aforward stroke, the spring 46 moves the actuator 40 to the retractedposition of FIG. 3 from the forward position shown in FIG. 4. Openingsin the armature portion 42 of the actuator 40 provide passage for mediumto pass and, thus, reduce viscous drag on the actuator 40.

As the actuator 40 retracts, the piston portion 44 of the actuator 40 isretracted relative to the valve member 66, such that a piston chamber 65volume is formed between the end of the piston portion 44 and the valvemember 66. The formation of the piston chamber 65 volume creates anegative pressure which draws infusion medium from the volume 51 of thecover member 50, through the annular space between the piston portion 44and the wall of the channel 35, and into the piston chamber 65.

In the retracted position, a gap is formed between each of the annularpole surfaces 91 and 93 separated by the inner and outer walls 90 and 92of the coil cup 32 and the respective annular surfaces of the inner andouter pole sections 49 and 47 of the actuator's armature portion 42. Inparticular, with reference to FIG. 3, a first gap 94 is formed betweenthe annular pole surface 91 of the inner cup wall 90 and the annularsurface of the inner pole section 49. A second gap 95 is formed betweenthe annular surface 93 of the outer cup wall 92 and the annular surfaceof the outer pole section 47.

When the coil 38 is energized, the actuator 40 is forced in thedirection to close the gaps 94 and 95 and moves to its forward position(FIG. 4) under the influence of electromagnetic flux generated by theenergized coil. In particular, the coil may be energized by passingelectrical current through the coil conductor to create electromagneticflux. This current is created by application of an electrical potentialprovided by a power source (e.g., discharge of a capacitor).

The electromagnetic flux defines a flux path through the coil cup walls,across the gaps 94 and 95, and through the armature portion 42 of theactuator 40. The electromagnetic flux provides an attraction forcebetween the annular surfaces 91 and 93 of the coil cup 32 and theannular surfaces 47 and 49 of the armature portion 42 to overcome thespring force of spring 46 and draw the armature 42 toward the coil cup32. As the armature portion 42 of the actuator is drawn toward the coilcup 32, the piston portion 44 of the actuator is moved axially throughthe channel 35 in the direction toward the outlet chamber 64.

With the coil energized, the piston portion 44 continues to move underthe action of the armature portion 42, until a mechanical stop isreached, for example, mechanical contact of the actuator 40 with barrier48, a portion of the housing 30, or cover member 50. Under somecircumstances (e.g., when a catheter connected to the outlet isblocked), the motion of the armature portion may only continue until theback pressure of the fluid overcomes the electromagnetic force providedby energizing the coil 38 (e.g., an incomplete delivery of medium). Thepresent invention provides one or more various techniques for detectingthe end of a pump stroke, or, in other words, for example, when thepiston portion 44 stops moving by a mechanical stop.

The movement of the piston portion 44 towards the stopping point reducesthe volume of the piston chamber 65 and increases the pressure withinthe piston chamber until the pressure is sufficient to overcome theforce of the valve spring 68. As the valve spring force is overcome bythe pressure within the piston chamber, the valve member 66 is movedtoward an open position, away from the opening between the pistonchamber 65 and outlet chamber 64. When the valve member 66 is in theopen position, medium is discharged through the outlet chamber 64 andoutlet 28 (see FIG. 2).

When the coil is deactivated (e.g., power is removed from the coil) andthe piston portion 44 is moved back to its retracted position, thepressure in the piston chamber 65 reduces, and the valve member 66 isreseated under the action of valve spring 68. This prevents fluid fromflowing back into the electromagnetic pump, through the outlet 28. Inaddition, a negative pressure is created in piston chamber 65 to drawmedium into the chamber for the next forward pump stroke.

In this manner, energization of the coil 38 to move the actuator 40 toits forward position (FIG. 4) causes a measured volume of medium to bedischarged through the outlet 28. As described herein, when the coil 38is de-energized, the actuator 40 is returned to the retracted position(FIG. 4) under the force of spring 46, and an additional volume ofmedium is drawn into the piston chamber 65 for the next dischargingoperation. Accordingly, the coil 38 may be energized and de-energized bya controlled electronic signal, where the control signal actuateselectromagnetic pump 20 to discharge a measured volume, or bolus, ofmedium. The controlled electronic signal, in one or more embodiments ofthe present invention, is provided by an electronic control system suchas that shown generally in FIG. 1, and of which one or more embodimentsare described further with reference to FIG. 5.

When the actuator 40 is stopped, for example, by mechanical stopstructure, or in any other manner, the coil current/voltage relationshipchanges. In the present invention, control electronics are provided todetect the end of the pump stroke based on sensed electricalcharacteristics associated with the electromagnetic pump 20.

In one or more embodiments according to the present invention, controlelectronics (e.g., such as those shown and described herein withreference to FIG. 5) are connected to detect the end of a pump stroke(e.g., using a first flux derivative algorithm or a back EMF algorithm).When such detection occurs, the coil 38 may be de-energized. In thismanner, the coil 38 may be energized for only as long as theelectromagnetic flux generated by the coil 38 is providing useful work.Once the actuator motion is stopped at the end of the pump stroke, andno further useful work is provided by the electromagnetic flux, the coil38 may be deactivated to reduce or minimize power consumptionrequirements of the electromagnetic pump 20.

FIG. 5 shows a generalized block diagram of an illustrative embodimentof an electronic control system 100 that may be connected to theelectromagnetic pump 20 for control thereof. The electronic controlsystem 100 includes a power source 110 connected to selectively energizethe coil of the electromagnetic pump 20, wherein the power source 110applies a source electrical potential to the coil to pass a coil currenttherethrough.

The electronic control system 100 further includes control electronics120 for receiving one or more sensed signals to be used in the detectionof the end of a pump stroke. The control electronics 120 includes acontroller 126 for controlling a switch device 128 to energize andde-energize the electromagnetic pump 20. The control electronics 120further include a current sense device 122 and a voltage sense device124 for providing information to controller 126 for use thereby indetection of the end of a pump stroke.

In one or more embodiments, the power source 110 includes a power supply112 connected to a capacitor 114 for charging the capacitor 114.Further, in one or more embodiments, the power source 110 includes apower supply 112 operatively connected via a switching device 116 to acapacitor 114 for selectively charging a capacitor 114 under control ofthe control electronics 120.

In one or more embodiments, the power supply 112 is connected to chargethe capacitor 114, and the capacitor 114 is connected to selectivelydischarge power to the coil of the electromagnetic pump 20. The chargedcapacitor 114 can provide a generally fast response power pulse to thecoil, on command or when otherwise desired.

The electronic control system 100, including the control electronics120, may be implemented, for example, on a single circuit board, or inany other manner. For example, in one or more embodiments, theelectronic control system may be implemented with the components asdiscrete units, and electrically connected together for operation.

In one or more embodiments, the power source 110 includes a portable,depletable power storage device, such as a battery. The use of portablepower supplies, such as batteries, may be advantageous in the context ofthe application, such as when the electromagnetic pump is intended to beportable (e.g., in implanted or portable external infusion devices).However, in one or more other embodiments, other forms of power sourcessuitable for other applications, including non-portable andnon-depleting power sources, may be employed.

Control electronics 120 control the charging and discharging of thecapacitor 114 and provide one or more additional functions as describedherein. For example, control electronics 120 provide for the operationof any detection processes as well as determination processes describedherein. The control electronics 120 may comprise one or moreprogrammable processors, logic circuits, or other hardware, firmware, orsoftware components configured for implementing functions as describedherein. One will recognize that various embodiments may be employedusing suitable hardware, firmware, or programmable processorimplementations to accomplish the functions described herein carried outby control electronics 120.

The control electronics 120 control the discharge of power from thecapacitor 114 to the coil of the electromagnetic pump 20, as needed ordesired for operating the electromagnetic pump 20, by selectivelycoupling or decoupling the capacitor 114 to the coil thereof. As shownin FIG. 5, the capacitor 114 is connected to the coil of theelectromagnetic pump 20 through an electronic switch device 128 of thecontrol electronics 120.

One will recognize that any suitable switch device capable of providingsuch connection may be used according to the present invention. Forexample, in one or more embodiments, the switch device may take the formof a field effect transistor (FET) or a junction transistor that iscontrolled, for example, by controller 126, to close and/or open whencommanded. One will recognize that any suitable electronic orelectromagnetic switch configurations, junction transistors, relays, orthe like, may be employed as the switch device 128. For example, byapplying a control signal to the switch device 128, the switch device128 may be closed to connect the capacitor 114 to the coil and allow thecapacitor 114 to discharge.

Controller 126 may also provide a control signal for operating a switchdevice 116 located between the power supply 112 and the capacitor 114 toselectively control the charging of the capacitor 114 by the powersupply 112. The switch device 116 may be of any suitable form, such asdescribed herein with respect to switch device 128, and, in one or moreembodiments, may be a FET device. By applying a suitable signal to theswitch device 116, the switch device 116 may be selectively closed tocharge the capacitor 114 or selectively opened to terminate suchcharging.

The control electronics 120 may be programmed or otherwise configured togenerate signals to control the opening or closure of switch device 128upon the occurrence of one or more various events. For example, switchdevice 128 may be closed upon the need for delivery of an infusionmedium into the infusion environment (e.g., initiate a pump stroke todeliver the infusion medium). Further, for example, such events mayinclude opening the switch device 128 upon the expiration of apredetermined time period if, for example, detection of an end of pumpstroke does not occur. Yet further, for example, switch device 128 maybe closed to initiate a pump stroke and opened upon detection of an endof pump stroke. One will recognize that any number of events may occurto control pumping action by the electromagnetic pump 20 as determinedby the control electronics 120.

Upon closure of the switch device 128, as shown in FIG. 5, the capacitor114 is electrically coupled to the coil of the electromagnetic pump 20.If the capacitor 114 is charged when the switch device 128 closes, thecharged capacitor 114 would discharge to energize the coil of the pump20. As described herein, when the coil is energized, the electromagneticpump actuator is caused to move to a forward position, for example,against a mechanical spring force. The actuator may abut a stop surfaceor the like at the actual end of the forward stroke, or, in other words,fail to move any further in a forward direction as a result of a backforce on the piston of the actuator of the electromagnetic pump 20.

Upon opening of the switch device 128, the capacitor 114 is electricallydecoupled from the coil of the electromagnetic pump 20. After the switchdevice 128 is opened, energy in the coil dissipates and the mechanicalspring force returns the actuator of the electromagnetic pump to itsretracted position. The switch device 116 may then be closed to allowthe capacitor 114 to recharge for subsequent pump stroke operation. Inthis manner, the capacitor 114 is controlled to charge and discharge toprovide electrical energy to the coil of the pump 20 as needed to effecta pump stroke operation (e.g., a plurality of pump strokes).

A graph of an example voltage diagram for a capacitor 114 is shown inFIG. 6. With reference to FIG. 6, the voltage V_(c) across the capacitor114 (i.e., source voltage U_(source) across the capacitor 114) risesduring charging to its fully charged level V₁ from its previouslycharged level V₂. To effect a pump stroke operation, a control signal isprovided by the control electronics 120 to turn on switch 128 at point142 in FIG. 6.

Once the switch device 128 is closed (i.e., turns on), the capacitor 114discharges and the source voltage U_(source) or voltage V_(c) across thecapacitor drops. However, prior to the capacitor 114 reaching a fullydischarged state, the control electronics 120 detects an end of pumpstroke and opens (i.e., turns off) the switch device 128, for example,at point 144 in FIG. 6. The broken line portion of FIG. 6 shows thevoltage across the capacitor 114 had the switch device 144 remainedclosed to completely discharge the capacitor. However, because theswitch device 128 is opened prior to full discharge of capacitor 114,the source voltage across the capacitor remains at level V₂, above thefully discharged level.

While some leakage may occur before the next charging operation, thevoltage across the capacitor 114 is at about the level V₂ or slightlylower, at point 146 in FIG. 6, when switch 116 is closed to recharge thecapacitor 114. Once the capacitor 114 is fully charged, as shown atpoint 148 in FIG. 6, the switch 116 may be opened and, as shown at point150, the switch 128 may be closed to effect another pump operation.Thus, by controlling the capacitor to discharge partially, but notfully, for each pump stroke operation, the voltage across the capacitor114 may have characteristics similar to that shown in FIG. 6.

Because the voltage V_(c) across the capacitor 114 remains at or aboutthe level. V₂ (above the fully discharged level) after its dischargeduring a pump stroke, the amount of energy needed to recharge thecapacitor 114 to the level V₁ is less than would be required had thecapacitor 114 been fully discharged. By selecting the size of thecapacitor 114 and the levels V₁ and V₂, suitable power may be providedto the coil of the electromagnetic pump 20 during the discharge (betweenpoints 142 and 144) to effect a pump stroke operation, while significantpower savings may be achieved during the recharging period (betweenpoints 146 and 148) as compared to charging a fully dischargedcapacitor. As such, detection of the end of the pump stroke such thatcontrol electronics 120 may open switch device 128 and de-energize thecoil of the electromagnetic pump 20 is important to reducing powerconsumption.

In other words, if detection of pump stroke does not occur, dischargemay continue until the capacitor is fully discharged, or until atime-out corresponding to a time when it is known that the pump strokewould be completed. In such situations, energy may be wasted. In otherwords, if the capacitor 114 continues to discharge power to the coil ofthe electromagnetic pump 20 after the actuator reaches the end of itsstroke, such continued discharge of power will not produce any furthermovement of the pump actuator and, thus, will be wasted. As such,according to one or more embodiments of the present invention, the pointat which the capacitor 114 stops discharging power to the coil of theelectromagnetic pump 20 is controlled to occur at the detection of theend of the actual stroke of the pump 20.

However, in one or more other embodiments, detection of the end of pumpstroke according to the present invention may be used for one or moreother applications. For example, such detection may be used to terminatethe discharging of power to the coil at a time prior to the actual endof the pump stroke.

FIG. 7 shows a graphical representation of the coil current during apump stroke. In FIG. 7, the solid line represents current passingthrough the coil of the electromagnetic pump 20. The current graph ofFIG. 7 shows the point 242 at which the capacitor 114 begins dischargingcurrent to the coil. A period of time prior to point 242 may involve acircuit warm-up period. Point 254 in FIG. 7 represents the time in whichthe capacitor 114 is cut off.

A capacitor cut off point 254 is determined by the detection of the endof the pump stroke. As shown in FIG. 7, a sharp rise (or inflection) ora change in direction of the current graph of FIG. 7 indicates actuatordeceleration that occurs at the actual end of the pump stroke. As such,such a current inflection in the coil current waveform could be detectedby control electronics 120 so as to provide an indication of the end ofstroke for use in opening switch 128 and de-energizing the coil ofelectromagnetic pump 20. The current through the coil may be provided tocontrol electronics 120 by a current sense device 122 as shown in FIG.5.

However, in one or more circumstances, the current waveform tends to besensitive to the inflection point shape and also tends to be difficultto detect when the capacitor discharges. Note, however, that the currentthrough the coil reaches a peak 256 during capacitor discharge and priorto the inflection point 253 of a pump stroke.

The control electronics 120, according to the present invention, usesthe sensed coil current (e.g., sensed using current sense device 122)and also a voltage measurement representative of the source voltageU_(source) (e.g., voltage V_(c) applied to the coil) applied to the coilof the electromagnetic pump 20 (e.g., as sensed or otherwise measured byvoltage sense components 124) to detect end of pump stroke. In one ormore embodiments, such measurements are also used to provide strokeposition information. As shown in FIG. 5, the source voltage may betaken as a measurement across the coil of the electromagnetic pump 20.Further, the current sensing components may be positioned between thecoil of the pump 20 and ground to measure the current passing throughthe coil of the pump 20.

One will recognize that any suitable measurement or sense devices may beutilized to provide coil current information as well as source voltageinformation to the control electronics 120 for use in accordance withthe present invention. The present invention is not limited to anyparticular design of providing such information to controller 126.

The controller 126 receives both source voltage measurements and currentsensed measurements according to the present invention. The controller126 then operates on such measurements using one or more variousalgorithms to detect end of pump stroke. According to one or moreembodiments, and which shall be described with reference to FIG. 8, afirst flux derivative algorithm may be used to detect end of strokeaccording to the present invention.

FIG. 8 shows exemplary waveforms for one exemplary electromagnetic pump.The source voltage or capacitor voltage waveform 300 (i.e., a measuredvoltage) is shown by line 300. In other words, in this particularexemplary embodiment, the capacitor starts discharging between 2 to 2.5volts. This capacitor voltage can be sensed at or otherwise obtained bytaking one or more measurements over time, and provided to thecontroller 126.

Also, as shown in FIG. 8, a coil current passing through the coil of theelectromagnetic pump is shown by the dashed waveform 301. The coilcurrent waveform 301 may be provided to the controller 126 by thecurrent sense device 122, such as shown in FIG. 5, by sensing the coilcurrent over time. With the coil current and capacitor voltage beingprovided over time, a first flux derivative waveform may bemathematically calculated according to the following equation:

U_(source)−(R_(coil)·I_(coil))

where U_(source) is the source voltage, R_(coil) is the coil resistance,and I_(coil) is coil current. This particular equation results in awaveform over time that represents the first flux derivative or thechange in flux with respect to time or dFlux/dt. As shown in FIG. 8, thefirst flux derivative waveform 302, calculated as indicated herein,includes a trough 308 generally corresponding to current peak 305 of thecurrent waveform 301, and a peak 309 that is indicative of the end ofthe pump stroke. As shown in FIG. 8, this particular current waveform301 does not include a discernible current inflection point at the endof pump stroke in the region 306 of the coil current waveform 301. Thisis quite unlike the readily apparent current inflection point shown inFIG. 7. In other words, first flux derivative waveform 302 clearly showsa peak 309 corresponding to the end of the pump stroke that can bedetected according to the present invention while a coil currentinflection may or may not be detectable in region 306 of the coilcurrent waveform 301.

FIGS. 9 and 10 show a comparison between two pump stroke illustrations.In FIG. 9, it is illustrated that the first flux derivative waveform 320for a free piston (i.e., that is allowed to moved) includes a peak point322 that corresponds to an inflection point 324 of the current waveform326, both of which (i.e., the peak 322 and inflection point 324) arerepresentative of the end of pump stroke. However, FIG. 10 shows a graphrepresentative of a case where the inflection point of the currentwaveform 334 is hardly discernible, whereas the peak 336 of the firstflux derivative waveform is clearly apparent and easily detectable. Thegraph of FIG. 9 further includes a position waveform 340 indicative of aposition of the actuator of the pump (e.g., a position that staysvirtually the same after the end of stroke is reached). Further, a firstflux derivative waveform 342 where the piston is blocked (e.g.,prevented from moving) as opposed to being in a free state is alsoshown. When the piston is blocked, no inflection points in either thefirst flux derivative waveform occur. Further, FIG. 10 includes a sourcevoltage waveform 344, as well as a position waveform 346 (e.g.,indicative of the position of the actuator of the pump).

As such, the calculated first flux derivative waveform may be used todetect end of pump stroke for determining the time to de-energize thecoil of electromagnetic pump 20. The control electronics 120 fordetecting the end of pump stroke based on the first flux derivativewaveform may be carried out in various ways. In one or more embodiments,the control electronics 120 calculates the first flux derivativewaveform (e.g., waveform 302 of FIG. 8) over time based on the sensedsource voltage and sensed coil current. Peak detection would then beused to detect a peak (e.g., peak 309 in FIG. 8) in the first fluxderivative waveform as calculated over time which corresponds to the endof a pump stroke.

In one or more embodiments, control electronics 120 may further analyzethe waveforms to more successfully perform peak detection. For example,in one or more embodiments, control electronics 120 may perform troughdetection to detect a minimum in the first flux derivative waveform(e.g., trough 308 in FIG. 8) prior to performing peak detection todetect a peak (e.g., peak 309 in FIG. 8) in the first flux derivativewaveform corresponding to the end of a pump stroke.

In one or more other embodiments, the control electronics may analyzethe sensed current (e.g., current waveform 301) in detecting the end ofa pump stroke. For example, in such embodiments, the control electronics120 may perform peak detection with respect to the sensed coil currentinformation to detect a peak in the coil current (e.g., peak 305, asshown in FIG. 8) prior to performing peak detection to detect a peak(e.g., peak 309 in FIG. 8) in the first flux derivative waveformcorresponding to the end of a pump stroke. In one or more circumstances,peak detection may be more easily implemented than trough detection. Onewill recognize that peak detection and trough detection are clearlyknown to one skilled in the art and may be implemented in any particularsuitable manner.

With the end of stroke detected using the first flux derivativewaveform, the control electronics 120 may effectively control switchdevice 128 to stop discharge of capacitor 114 to the electromagneticpump 20. In other words, upon detection of the end of a pump stroke, thepower source 110 may be disconnected from the coil of electromagneticpump 20.

Yet further, in one or more embodiments, a back EMF voltage may becalculated using the coil current and the source voltage (U_(source)).The control electronics 120 calculates the back EMF voltage (e.g.,provides a back EMF waveform over time) according to the followingequation:

$U_{emf} = {U_{source} - {\left( {R_{coil} + R_{source}} \right) \cdot I_{coil}} - {{L_{coil} \cdot \frac{}{t}}I_{coil}}}$

where U_(emf) is the back EMF voltage, U_(source) is the source voltage,R_(coil) is the coil resistance, R_(source) is the source resistance,I_(coil) is coil current, and L_(coil) is coil inductance (e.g., set toa particular inductance value, such as the coil inductance at thebeginning of the stroke).

To use the calculated back EMF voltage to provide for detection of anend of a pump stroke, a back EMF limit value is identified correspondingto a completed pump stroke. For example, such a back EMF limit may bedetermined by repeated trial operation of an electromagnetic pump.

FIG. 11 shows a graphical representation of a calculated back EMFvoltage based on measurements taken over time for a plurality ofillustrative pump embodiments. Calculated back EMF waveforms (i.e.,calculated based on current and voltage measurements as opposed tosensed back EMF) are shown where no capacitor is used (waveform 360), aback EMF waveform 362 is provided where a 1470 microfarad capacitor isused, and waveform 364 is provided where a 470 microfarad capacitor isused at 25 psi. As shown in this particular illustrative calculated backEMF diagram, if a threshold limit value 366 of one (1) volt (orsomething slightly less than one, e.g., 0.75) is set as the back EMFlimit when it is know that pump stroke has ended, the calculatedwaveform 362 when compared to the threshold 366 would indicate an end ofpump stroke. The calculated back EMF waveform 360, where an infinitepower source is used clearly exceeds this limit as well. However, backEMF waveform 362 (where there is insufficient capacitor size and toolarge of a back pressure on the piston) does not exceed the limit andend of stroke would not be detected.

It will be recognized that the back EMF algorithm for detection of endof pump stroke may be used alone or it may be used in combination withthe first flux derivative algorithm, such as to validate an end ofstroke.

Yet further, in one or more embodiments, calculation of inductance fromthe sensed measurements (e.g., coil current and source voltage) may alsobe used, for example, at the end of a stroke and/or at the beginning ofa stroke, as inductance provides information with respect to theposition of the actuator (e.g., relative to the coil). For example, thefollowing inductance algorithm may be used by the control electronics tocalculate inductance at the end of the pump stroke with such calculatedinformation being used to determine whether the actuator is in fact at aparticular desired position at the end of pump stroke.

Based on the electromagnetic equation of the actuator:

$L_{coil} = {\frac{U_{source} - {\left( {R_{coil} + R_{source}} \right) \cdot I_{coil}} - {\gamma \cdot w_{pist}}}{\frac{}{t}I_{coil}}.}$

where U_(source) is the source voltage, R_(coil) is the coil resistance,R_(source) is the source resistance, I_(coil) is coil current, L_(coil)is coil inductance, γ is the electromagnetic coupling factor between theback EMF voltage and pole velocity, and ω_(pist) is piston velocity.

For a non-moving piston, since ω_(pist) is zero, it can be assumed that:

γ·ω_(pist)=0

FIG. 12 shows a graphical diagram of exemplary current, position, andinductance characteristics of one embodiment of a pump, where pump headpressure is zero and no capacitor is used for discharge. As shown inFIG. 12, the current waveform 380 shows an end of pump stroke at point382 as indicated by the current inflection at this point. When theelectrical potential is removed from the coil, the current through thecoil begins to fall to zero (i.e., point 386). The actuator positionwaveform 388 shows that about the time corresponding to the end ofstroke (i.e., point 382), the position of the actuator is thereaftersubstantially maintained.

At the end of the voltage pulse energizing the coil (i.e., point 384),the current falls to zero (i.e., point 386) and so does the actuatorforce. At this point, the piston starts to move back very slowly due tothe beginning of the refill phase of the pump. Since the current valuealso affects inductance, a point is selected where the inductance can becalculated. Although other points may be selected upon or afterdetection of end of stroke, one possible selection point is where thecurrent falls to zero since this condition is fulfilled in all externalconditions. However, inductance cannot be calculated after the end ofcurrent (EOC) has been reached since after this point, the currentvariation would tend to zero and the division by dI/dt would lead to anindetermination. Therefore, at least in one embodiment, the inductanceis windowed (e.g., measurements in a window of time are selected,buffered or otherwise retained) prior to EOC being actually reached. Forexample, the inductance may be windowed by a window width equal to theEOC time (e.g., time it takes the current to fall to zero after power isremoved from the coil at the end of stroke). Further, for example,inductance may be measured over a time period (e.g., before the EOC isreached) and the mean value over the time period (e.g., 2 milliseconds)may be used to remove noise from the calculated inductance.

As such, the inductance EOC (L_(coil) _(—) _(EOC)) is defined asfollows:

$L_{{coil}\_ {EOC}} = \frac{U_{source} - {\left( {R_{coil} + R_{source}} \right) \cdot I_{coil}} - {\gamma \cdot w_{pist}}}{\frac{}{t}I_{coil}}$

In other words, as shown in the graph of FIG. 12, such inductance EOC iscalculated, at least in one embodiment, around region 390.

The voltage level applied to energize the pump coil does not affect therelationship between the measured inductance EOC and the position of theactuator, nor does it appear that capacitor size affects thisrelationship.

A certain inductance EOC will be reached at the end of the stroke andwhen compared to a previously determined value or range of acceptablevalues of inductance EOC for a particular pump system (e.g., using alook up table correlating inductance to position of the actuator), itcan be determined if the actuator is actually at the desired position atthe end of the pump stroke. For example, if a problem with the pumpsystem occurs (e.g., catheter plugged, air bubbles are present, or apiston was cocked) the inductance EOC would not be as expected and aproblem could be detected with the pump system. In other words, suchinformation may be used for diagnostic purposes (e.g., determineposition of the actuator based on inductance).

Yet further, the inductance may also be measured at the beginning of thepump stroke when the piston is not moving as shown on the graph of FIG.12 at region 394. A calculation virtually the same as that shown abovefor inductance at the end of pump stroke is used. For example, the samenoise reduction methods, as well as windowing techniques may be used.

Such information at the beginning of the stroke may be used in a similarmanner as the information calculated at the end of pump stroke. Forexample, it can be determined whether the actuator is retracted all theway as it should be at the beginning of a stroke.

All patents and references cited herein are incorporated in theirentirety as if each were incorporated separately. This invention hasbeen described with reference to illustrative embodiments and is notmeant to be construed in a limiting sense. As described previously, oneskilled in the art will recognize that various modifications of theillustrative embodiments, as well as additional embodiments to theinvention and combinations of various elements and/or steps herein, willbe apparent to persons skilled in the art upon reference to thisdescription. It is therefore contemplated that the patent and claimswill cover any such modifications or embodiments that may fall withinthe scope of the present invention, as defined by the accompanyingclaims.

1-16. (canceled)
 17. An electromagnetic pump system comprising: anelectromagnetic pump comprising a coil that can be energized to producea pump stroke, wherein the electromagnetic pump further comprises anactuator moveable in response to the energization of the coil; a powersource connected to selectively energize the coil of the electromagneticpump, wherein the power source applies a source electrical potential tothe coil to pass a coil current therethrough; a voltage sense device forsensing the source electrical potential applied to the coil; a currentsense device for sensing the coil current; and control electronics tocalculate inductance of the coil as a function of sensed coil currentand source electrical potential when the actuator is not moving for usein determining position of the actuator.
 18. The system of claim 17,wherein the control electronics calculates(U_(source)−(R_(coil)+R_(source))*I_(coil))/d/dt I_(coil) for use indetermining position of the actuator.
 19. The system of claim 17,wherein the control electronics calculates inductance after detection ofend of stroke and prior to end of current in the coil.
 20. The system ofclaim 17, wherein the system is part of an implantable medical device.21. A method for use in controlling an electromagnetic pump, theelectromagnetic pump comprising a coil that can be energized by a powersource to produce a pump stroke and an actuator moveable in response tothe energization of the coil, wherein the method comprises: applying asource electrical potential to the coil to pass a coil currenttherethrough to provide a pump stroke; sensing the source electricalpotential applied to the coil; sensing the coil current; and detectingthe end of the pump stroke based on a change in flux over timecalculated as a function of sensed coil current and source electricalpotential.
 22. The method of claim 21, wherein detecting the end of thepump stroke comprises calculating U_(source)−(R_(coil)*I_(coil)) overtime corresponding to the change of flux over time, where U_(source) issource electrical potential, R_(coil) is the resistance of the coil, andI_(coil) is the coil current.
 23. The method of claim 22, whereindetecting the end of the pump stroke comprises performing peak detectionto detect a peak in U_(source)−(R_(coil)*I_(coil)) as calculated overtime corresponding to the end of a pump stroke.
 24. The method of claim22, wherein detecting the end of the pump stroke comprises performingtrough detection to detect a minimum in U_(source)−(R_(coil)*I_(coil))as calculated over time prior to performing peak detection to detect apeak in U_(source)−(R_(coil)*I_(coil)) corresponding to the end of apump stroke.
 25. The method of claim 22, wherein detecting the end ofthe pump stroke comprises performing peak detection to detect a peak inI_(coil) as sensed over time prior to performing peak detection todetect a peak in U_(source)−(R_(coil)*I_(coil)) corresponding to the endof a pump stroke.
 26. The method of claim 21, wherein selectivelyapplying a source electrical potential to the coil comprises connectingthe power source to the coil at the initiation of a pump stroke anddisconnecting the power source from the coil upon detection of an end ofthe pump stroke.
 27. The method of claim 21, wherein the method furthercomprises calculating inductance of the coil as a function of sensedcoil current and source electrical potential to verify position of theactuator.
 28. The method of claim 27, wherein calculating inductancecomprises calculating (U_(source)−(R_(coil)+R_(source))*I_(coil))/d/dtI_(coil).
 29. The method of claim 27, wherein the method furthercomprises calculating inductance after detection of end of stroke andprior to end of current in the coil.
 30. The method of claim 21, whereinthe pump stroke delivers infusion medium.
 31. A method for use incontrolling an electromagnetic pump, the electromagnetic pump comprisinga coil that can be energized by a power source to produce a pump strokeand an actuator moveable in response to the energization of the coil,wherein the method comprises: applying a source electrical potential tothe coil to pass a coil current therethrough to provide a pump stroke;sensing the source electrical potential applied to the coil; sensing thecoil current; and calculating inductance of the coil as a function ofsensed coil current and source electrical potential for use indetermining position of the actuator.
 32. The method of claim 31,wherein calculating inductance comprises calculating(U_(source)−(R_(coil)+R_(source))*I_(coil))/d/dt I_(coil).
 33. Themethod of claim 31, wherein the method further comprises calculatinginductance after detection of end of pump stroke and prior to end ofcurrent in the coil.